EFFECT OF ALUMINUM AND 6-BENZYLAMINOPURINE ON THE GROWTH OF THE EPICOTYL IN MUNGBEAN SEEDLINGS

Aluminium (Al) toxicity was studied for mungbean (Phaseolus aureus Rox b.) seedlings under controlled environmental conditions in a growth ch amber. Ten-day-old seedlings or cuttings (root removed) grew in dilute nutrient solution (pH 4.1) with Al levels and 6-benzylaminopurine (6- BA) concentrations for six days. Results showed that Al concentrations less than 2 mM had no significant effect on the length of the epicoty l in mungbean seedlings. Elongation of the epicotyl of intact seedling s was inhibited by 5 mM Al. The decrease in dry weight of the epicotyl was more evident than that in dry weight of hypocotyl, root, and prim ary leaves, indicating that epicotyl damage was greater than other org ans by Al toxicity. No significant difference was found in the length of epicotyl between seedlings with and without 6-3A treatment. But the re was a marked decrease in length of the epicotyl when cuttings were treated with 1 mM and 5 mM Al. Addition of 6-BA to the nutrient soluti on significantly increased the elongation of the epicotyl in cuttings treated with 0.05 mM and 1 mM Al. but only slightly in the cuttings tr eated with 5 mM Al. When the Al concentration was greater than 1 mM, t he concentration of soluble protein in epicotyl of seedlings was incre ased by the Al treatment. 6-BA significantly increased the concentrati on of soluble protein in the epicotyl of the seedlings with 0.05 mM or 1 mM Al treatment. The present results indirectly indicated that high concentrations of Al inhibited elongation of the epicotyl in mungbean seedlings not by the shortage of endogenous cytokinin export from the root tips to the shoots but by other toxicity mechanisms.